This invention relates to grinding machines and to grinding wheels for use in such machines for grinding notches in the edges of discs such as wafers of silicon for use in the construction of semi-conductor devices, and to methods of grinding edge regions of such discs so as to form notches therein. Since the notches are of relatively small dimensions relative to the size of the wafers, grinding wheels used to form such notches are commonly referred to as grinding pins.
A grinding machine for grinding discs is disclosed in WO97/48522 and incorporated herein by reference. WO97/48522 discloses use of a metal-bonded CBN or diamond wheel on a grinding machine to rough grind the edge of a disc, such as a semiconductor wafer, before use of a softer resin-bonded CBN wheel for finish grinding the disc edge and further describes an in situ technique for forming and re-forming a groove in the resin bonded CBN grinding wheel to grind the correct shape around the disc edge.
The machine also includes a small diameter grinding pin for grinding a notch of predetermined proportions around the edge of the ground disc.
British Patent Specification No. 2335620 discloses a grinding pin for notch grinding, for example for use in the machine described in WO 97/48522, the pin having a cylindrical region sufficiently long that a succession of profiled grooves for producing the notch can be formed, whereby as one such groove becomes too worn for further use one or more further grooves can be formed in the pin. One embodiment of pin described in the Specification is a pin having a metal bonded diamond section axially nearer the pin spindle and a resin bonded formable section axially more remote from the spindle. In use, a groove in the metal bonded section is used for rough grinding the notch and a groove formed in the resin bonded formable section is used for finish grinding the notch.
A problem with the aforesaid arrangement of the grinding pin is that of aligning the metal bonded and the resin bonded sections.
According to one aspect of the present invention, a grinding pin for notch grinding comprises a cylindrical region long enough for at least two profiled grooves to be formed thereon respectively in axially spaced sections of the cylindrical region, the section axially more remote from the pin spindle being a resin-bonded section of rough grit for rough grinding the notch and the section axially nearer the pin spindle being a resin-bonded section of fine grit for finish grinding the notch.
The invention overcomes the problem of aligning the respective sections to be used for rough and finish grinding the notch, because it is possible to use the same groove dressing or forming wheel, mounted on the same machine, to form both or all the grooves.
Preferably, the size of the grit for rough grinding the notch is between two and three times the size of the grit for finish grinding the notch.
Either or both of the rough grinding and finish grinding sections of the cylindrical pin, but especially the latter, may be long enough for one or more further grooves to be successively formed when the first groove becomes too worn for further use.
The invention also relates to a grinding machine, preferably a CNC grinding machine, having a work spindle, a grinding spindle able to carry a blank for the aforesaid grinding pin, the blank having a section of rough grit and a section of fine grit, and a forming wheel rotatable to form a notch-grinding groove in the rough grit section and a notch-finishing groove in the fine grit section.
The invention therefore also relates to a method of forming notches of rough grinding and notch-finishing grooves on the aforesaid grinding machine.
The forming wheel may be mounted on the same spindle as the workpiece.
The grinding material may be rough grit resin-bonded CBN or diamond in the case of the rough grinding section and fine grit resin-bonded diamond in the case of the finish grinding section.
The term xe2x80x9cresin-bondedxe2x80x9d, as used herein, includes bonding with a vitreous material.
It is to be noted that, in contrast to the disclosure of FIG. 7 of British Patent Specification No. 2335620, wherein a resin-bonded section is used in place of a metal-bonded section, it is preferable for the section for finish grinding to be nearer the pin spindle, i.e. the stiffer section of the pin.